The effects of skin aging on the appearance of the human face are well studied and documented in dermatology. Each individual's skin aging progression is dependent on both intrinsic and extrinsic factors. Intrinsic factors, like gender, race, and skin pigmentation, are genetically programmed and unique for each individual and can affect the rate of dermal thinning, loss of mechanical elasticity, and other well-characterized histological and bio-mechanical changes with age. Intrinsic factors affect both sun-protected and sun-exposed body sites. Extrinsic factors include an individual's diet, lifestyle, skin care habits and sun exposure history. Chronic sun exposure is well-known to accelerate the onset time and severity of skin aging (also called photoaging). All exposed body sites including the face have some degree of skin photoaging. (Gilchrest., B. Photodamage, Blackwell Science, Inc. 1995).
One of the most visually prominent features of aged facial skin is fine lines and wrinkles (Leyden J. J. “Clinical features of ageing skin”, Br. J. Dermatol Vol. 122, Suppl. 35, pp: 1-3, 1990) caused in part by the gradual alteration and loss of dermal connective tissues such as collagen and elastin, especially in sun-exposed areas of the body (Bailey, Molecular mechanisms of aging in connective tissues, Mech. Aging Dev., Vol. 122, No. 7, pp.: 735-755, 2001). Skin is a multilayered tissue with an outer stratum corneum (10-20 μm), a living epidermis (50-100 μm), a dermis (1-3 mm) and hypodermis composed primarily of adipocytes. The skin is connected to the underlying musculature via connective tissue and the muscles are attached to the skull bone.
With facial expressions such as smiling, muscles such as the zygomatic major and the obicularis oculi contract and the surface area of the skin shrinks around the eyes and on the cheek. Since skin is incompressible, when the surface area shrinks, the excess skin buckles and forms wrinkles perpendicular to the direction of contraction. The generation of ‘crows feet’ or ‘laugh lines’ around the eye are common examples of such wrinkles. When the muscles relax, the surface area returns to normal and the wrinkles disappear. Wrinkles that form and disappear in this way are called expressive, dynamic, or temporary wrinkles. Over time, the mechanical stress caused by repeated facial expression along the same skin groove eventually causes these temporary wrinkles to become visible without expression (Kligman et al., Br. J. Derm. 1985, 113:37-42). Wrinkles which are visible without facial expression are called permanent, persistent or static wrinkles. The conversion from temporary to persistent wrinkles is influenced by the structural integrity of the underlying dermal matrix proteins. The age-dependent loss in skin elasticity, which is accelerated by chronic sun exposure and smoking, weakens the dermal matrix structure and speeds up the onset time of permanent wrinkles. Importantly, each individual develops permanent facial wrinkles that are unique in length, width, depth and position on the face, as unique as their own fingerprints.
The ability to predict and visualize an individual's future facial skin wrinkling has utility in computer animation, facial recognition, missing person identification, entertainment, medicine and cosmetics. Various models have been employed to enable the realistic simulation of an aging face including geometric models, physically-based models, bio-mechanical models and image-based models (Hussein, K. H, Toward realistic facial modeling and re-rendering of human skin aging animation, Proceedings of the Shape Modeling International 2002, IEEE Computer Society, 2002). For visualization purposes, image-based models produce more realistic simulation than physical-based models. Image-based models typically use images of real people in various ways to simulate aging effects.
Several approaches have been taken to personalize aging simulation using image-based models so that it more accurately depicts a particular person's future aged appearance. For example, aging algorithms have been developed based on a population cohort of images combined with published data regarding facial changes associated with aging in order to simulate an aged appearance of an individual (Hysert P E et al. “At Face Value: age progression software provides personalized demonstration of the effects of smoking on appearance.” Tobacco Control, Vol. 12, pp: 238-240, 2003). A limitation of this method is that the aged image is a reflection of population norms, and does not necessarily reflect the individual's unique aging process.
Boissiux et al. developed an image-based model for simulating skin aging whereby generic masks of pre-computed wrinkles are applied as textures on a 3D model of a person's face. Eight basic masks are employed and the particular mask used is matched to the person's gender, shape of face and type of expression being simulated (Boissiux et al. “Simulation of skin aging and wrinkle with cosmetic insight”, Computer Animation and Simulation, pp 15-27, 2000). Because of its dependence on a generic mask, this approach is also limited in its ability to accurately predict each person's unique skin features that will appear with age.
U.S. Pat. No. 7,020,347 to Zhang et al. entitled “System and method for image-based surface detail transfer,” describes a method for transferring the geometric details of an old face onto that of a young face in order to make the young face look old. Conversely, the surface details of a young face can be transferred to that of an old to make an old face look young. This approach is limited by the fact that the aging features of the old face will not be exactly the same features that the young face will eventually realize.
An object of the present invention is to provide a method to more accurately predict and visualize an individual's future facial skin wrinkling unique to that particular person. It is a another object of the present invention to provide a method to predict an individual's facial skin wrinkling at a specific point in time in the future based on, for example, that person's sex, skin type, and/or ethnicity. It is still another object of the present invention to provide a method to predict and visualize an individual's future skin wrinkling with or without a cosmetic or dermatological treatment.